1. Field of the Invention
This invention relates to a telephone intercommunication system incorporating an improved dialing arrangement, and more especially to such a system in which each telephone station of a private intercommunication system may have direct access to one or more external exchange lines and is provided with the facility for direct dialing or keying of external calls.
2. Description of the Prior Art
According to one feature of such telephone intercommunication systems, dialing of either internal extensions within the system itself or of external calls via an exchange line in provided for by a common keypad which is arranged on the one hand to activate a buzzer of an internal extension, and on the other to activate an integrated circuit chip for generating the necessary coded switching signals for out-dialing to an external exchange. Such signals may comprise dial pulses or multi-frequency tone signals, depending on the type of exchange concerned. The alternative functions of the common keypad are selected in accordance with the switched state of the telephone speech circuit, i.e., depending on whether it is connected to an internal speech channel or an external exchange line.
In such previous telephone exchange systems, it has been necessary to incorporate an integrated circuit for generating the coded signals for out-dialing, in each of the extension telephone stations of the system. Such an arrangement involves a duplication of components which renders the system relatively costly.
It is accordingly an object of the present invention to provide a telephone intercommunication system of the type initially referred to, which is of simpler and more economic construction than has hitherto been achieved.